1. Field of the Invention
The present invention relates to a technology of reproducing data which is digitally recorded or digitally transmitted, particularly to a data reproducing system using PRML (Partial Response Maximum Likelihood) for executing partial response equalization suitable for a characteristic of a transmission path.
More in details, the present invention relates to an apparatus and a method of equalizing a waveform for reducing an equalization distortion by equalizing the waveform in a desired frequency characteristic, particularly to an apparatus and a method of equalizing a waveform for executing equalization by using PR1 (Partial Response Class 1) of a low frequency region emphasizing type to thereby realize accurate data detection.
2. Description of the Related Art
In the technical field of information processing, much data is handled after having been digitized. That is, softwares necessary for starting an information processing system or controlling operation thereof or data formed on the system are stored in a magnetic disk type recording apparatus such as a hard disk drive as a digitized file or are transmitted via a network such as LAN (Local Area Network) or the like. On the other hand, in order to reutilize data, analog waveform data read from a magnetic disk or analog waveform data received from a transmission path needs to digitally reproduce accurately.
Originally, in record data or transmission data, binary data comprising 0 and 1 is expressed in a square hit form. For example, in a magnetic disk type recording apparatus, data is reproduced by using a rise pulse and a fall pulse of a square wave by differentiating a signal read from a magnetic head. However, the rise and the fall pulse waves are accompanied by waveform rounding. When a recording density is promoted, an interval between the pulse waves becomes narrow by that amount and the pulse waveforms interfere with each other to thereby make difficult reproduction of data.
For example, due to an increase in the number and size of files handled by an information processing apparatus, the need for a large capacity formation and promotion of a record density with regard to a magnetic disk type recording apparatus such as a hard disk is required. The increase in the record density signifies a reduction in a volume of a magnetic member per bit of data. Accordingly, magnetic force is naturally reduced, a reproduced signal is weakened and noise is magnified relatively. Therefore, in the technical field of digital recording, a technology for accurately reproducing data from a weak reproduced signal becomes indispensable.
Such a problem of digital reproduction naturally exists not only in a digital recording apparatus but also in a digital communication apparatus.
In order to realize further accurate data reproduction, a technology referred to as so-to-speak PRML (Partial Response Maximum Likelihood) has been used widely. This is constituted by combining two data reproducing systems of a partial response system and a Viterbi decoding system. The partial response system provides equalization, that is, operation of neatly arranging a waveform of a reproduced signal. Further, the Viterbi decoding system is provided with maximum likelihood, that is, operation of reproducing data string which is mostly probable in view of the probability.
In an extremely simple expression, equalization of a waveform is realized by isolating respective pulse waves by exalting a high frequency component of a reproduced waveform. However, when the high frequency component is extremely exalted, in accordance therewith, rise at a low frequency is also amplified. Therefore, there has widely been adopted a system of permitting waveform interference partially, which is referred to as partial response.
The partial response is provided with a plurality of classes indicating equalization references of PR4 (Partial Response Class 4) and PR1 (Partial Response Class 1). PR4 is provided with an equalized frequency characteristic of (1xe2x88x92D) (1+D) and is expressed in an equivalent block diagram as shown by FIG. 6A. Further, PR1 is provided with an equalized frequency characteristic of (1+D) and is expressed in an equivalent block diagram as shown by FIG. 6B. Incidentally, shown in FIGS. 6A and 6B designates an operator expressing delay of 1 channel clock. Therefore, PR4 signifies (1xe2x88x92D) (1+D) =1xe2x88x92D2, that is, a difference is calculated from a current component by square of a component forward by 1 clock, further, PR1 signifies to add the component forward by 1 clock to the current component.
It is general to constitute a PR4 equalizer by using a 7 pole 2 null equiripple filter. This is derived from that the equiripple filter is provided with a flat phase characteristic and setting of parameters is comparatively easy. With regard to the PR4 equalizer, for example, there is a description in xe2x80x9cA 27 MHz Programmable Bipolar 0.05; Equiripple Linear-Phase Lowpass Filterxe2x80x9d by Greet A. De Veirman et al, (1992 IEEE International Solid-State Circuits Conference).
In contrast thereto, PR1 equalization can arrange a waveform by reducing a degree of exalting a frequency component and is suitable for a magnetic disk having a high linear density, that is, high record density. Since PR1 executes a low frequency region emphasizing type equalization, conventionally, a PR1 equalizer is often constituted by combining an integral equalizer with a filter for emphasizing a high frequency region as well as attenuating a component at a vicinity of a Nyquist frequency, a filter for correcting group delay or the like.
However, in the case in which the PR1 equalizer is constituted by a combination of such many filters, it is not easy to flatten a phase at a high frequency region and accordingly, it is difficult to promote the equalization characteristic. Further, although a degree of freedom is enhanced by an amount of increasing parameters, on the other hand, it is very difficult to set optimum parameters.
According an example of a conventional PR1 equalizer, the PR1 equalizer is constituted by a combination of a highpass filter and a 6-th order lowpass filter. In this industry, generally, an amount of calculation for setting parameters of a circuit is expanded exponentially in accordance with an order degree provided to the circuit and it is very difficult to calculate an optimum solution of such an high order PR1 equalizer. Further, a circuit for constituting the equalizer becomes large-scaled in accordance with the order degree and power consumption is increased by that amount.
In order to realize application of a PR1 equalizer suitable for a high linear density to a data reproducing apparatus, this must be realized by a simple circuit constitution. Further, it seems to be necessary that optimum parameter setting of PR1 equalization is calculated easily in accordance with a simple algorism.
It is an object of the present invention to provide an excellent data reproducing system using PRML (Partial Response Maximum Likelihood) for executing partial response equalization suitable for a characteristic of a transmission path.
It is a further object of the present invention to provide an excellent waveform equalizing apparatus and its method for enabling accurate data detection by reducing equalization distortion by equalizing a waveform to a desired frequency characteristic.
It is a further object of the present invention to provide an excellent waveform equalizing apparatus and its method for executing equalization by using PR1 (Partial Response Class 1) of a low frequency region emphasizing type.
It is a further object of the present invention to provide an excellent waveform equalizing apparatus and its method for reducing a circuit scale and realizing a PR1 equalizer by reducing power consumption.
The present invention has been carried out in consideration of the above-described problem and a first aspect thereof is a waveform equalizing apparatus for equalizing an input waveform to an equalization reference of Partial Response Class 1, wherein a phase variation at a high frequency region is prevented by executing emphasis of the high frequency region and steep attenuation at a vicinity of a Nyquist frequency by using a phase flat filter.
By positively utilizing the operational characteristic of the phase flattening filter which is one of constituent elements of the waveform equalizing apparatus, while restraining the phase variation of the input waveform at the high frequency region, emphasis of the high frequency region and the steep attenuation at the vicinity of the Nyquist frequency can be realized.
Further, a second aspect of the present invention is a phase equalizing apparatus which equalizes an input waveform to an equalization reference of Partial Response Class 1 by a combination of an integrator for emphasizing a low frequency region and an equalizer for equalizing to an equalization reference of Partial Response Class 4.
It is known that in the high frequency region at the vicinity of the Nyquist frequency, emphasis of the amplitude characteristic is known to be smaller in Class 1 (PR1) than in Class 4 (PR4) of partial response. Hence, in the case of the waveform equalizing apparatus according to the second aspect of the present invention, the waveform equalizing apparatus satisfying the PR1 equalization reference is constituted by the combination of the integrator for emphasizing the low frequency region and the filter constituted for PR4. By such a constitution, the circuit scale is reduced more than in the conventional PR1 equalizer and power consumption can further be reduced.
Further, a third aspect of the present invention is a method of optimizing a waveform equalizing apparatus having an equalization reference of Partial Response Class 1 constituted by a combination of an integrator for emphasizing a low frequency region and an equalizer for equalizing to an equalization reference of Partial Response Class 4, which individually optimizes respective parameters of the integrator and the equalizer, and a waveform equalizing apparatus optimized by the optimizing method.
The conventional Partial Response Class 1 (PR1) equalizing apparatus is constituted by a combination of many filters and therefore, a number of parameters to be set is large and optimization is difficult. Further, flattening of high frequency phase is not easy and it is difficult to promote equalization characteristic. In contrast thereto, according to the third aspect of the present invention, by facilitating flattening of the high frequency phase by using the PR4 equalizer and individually optimizing the respective parameters of the integrator and the equalizer, calculation load for setting the parameters can be alleviated.
Further, a fourth aspect of the present invention is a method of optimizing a waveform equalizing apparatus having an equalization reference of Partial Response Class 1 constituted by a combination of an integrator for emphasizing a low frequency region and an equalizer for equalizing to an equalization reference of Partial Response Class 4, comprising:
a first step of optimizing a parameter provided to the equalizer to satisfy the equalization reference of Partial Response Class 4; and
a second step of optimizing a parameter provided to the integrator by using the parameter optimized by the first step,
and a waveform equalizing apparatus optimized by the optimizing method.
According to the fourth aspect of the present invention, flattening of the high frequency region phase is facilitated by using the PR4 equalizer, a total of the waveform equalizing apparatus is optimized in accordance with a procedure of firstly optimizing the parameter provided to the PR4 equalizer and successively optimizing the parameter provided to the integrator and accordingly, the calculation load for setting the parameters can be alleviated.
More specifically, the waveform equalizing apparatus according to the aspect is constituted by five parameters of a cutoff frequency of the low frequency region removing filter, gain and a cutoff frequency of the integrator and a boost amount and a cutoff frequency of the equiripple equalizer for PR4. Although a solution is not converged when all of the parameters are intended to optimize simultaneously, by following the above-described procedure, the equalizing apparatus having a desired characteristic can be provided by a comparatively small calculation amount.
Further, a fifth aspect of the present invention is a method of optimizing a waveform equalizing apparatus having an equalization reference of Partial Response Class 1 constituted by a combination of an integrator for emphasizing a low frequency region and an equalizer for equalizing to an equalization reference of Partial Response Class 4, comprising:
a first step of optimizing a parameter provided to the equalizer to satisfy the equalization reference of Partial Response Class 4;
a second step of optimizing a parameter provided to the integrator by using the parameter optimized by the first step; and
a third step of further optimizing the parameter provided to the equalizer by using the parameter optimized by the second step,
and a waveform equalizing apparatus optimized by the optimizing method.
According to the fifth aspect of the present invention, flattening of the high frequency region phase is facilitated by using the PR4 equalizer and firstly, the parameter provided to the PR equalizer is optimized, successively, the parameter provided to the integrator is optimized and thereafter, the parameter provided to the PR4 equalizer is further optimized. As a result, higher equalization characteristic can be realized.
Further, a sixth aspect of the present invention is a program providing medium which is a program providing medium for materially providing a computer program operated on a computer system, comprising:
a first step of optimizing a parameter provided to the equalizer to satisfy the equalization reference of Partial Response Class 4; and
a second step of optimizing a parameter provided to the integrator by using the parameter optimized by the first step;
for optimizing a waveform equalizing apparatus having an equalization reference of Partial Response Class 1 constituted by a combination of an integrator for emphasizing a low frequency region and an equalizer for equalizing to an equalization reference of Partial Response Class 4.
The sixth aspect of the present invention is the program providing medium for materially providing the computer program for realizing the method of optimizing a waveform equalizing apparatus according to the fourth aspect to the computer system. That is, there is defined a cooperative relationship between the computer program and the provided medium in view of structure or in view of function, in other words, by introducing the computer program to the computer system, the cooperative relationship is achieved on the computer system and operation and effect similar to that in the fourth aspect of the present invention can be achieved.
A seventh aspect of the present invention is a program providing medium which is a program providing medium for materially providing a computer program operated on a computer system, comprising:
a first step of optimizing a parameter provided to the equalizer to satisfy the equalization reference of Partial Response Class 4;
a second step of optimizing a parameter provided to the integrator by using the parameter optimized by the first step; and
a third step of further optimizing the parameter provided to the equalizer by using the parameter optimized by the second step;
for optimizing a waveform equalizing apparatus having an equalization reference of Partial Response Class 1 constituted by a combination of an integrator for emphasizing a low frequency region and an equalizer for equalizing to an equalization reference of Partial Response Class 4.
The seventh aspect of the present invention is the program providing medium materially providing the computer program for realizing the method of optimizing the waveform equalizing apparatus according to the fifth aspect to the computer system. That is, there is defined a cooperative relationship between the computer program and the provided medium in view of structure or in view of function and by introducing the computer program to the computer system, operation and effect similar to that in the fifth aspect of the present invention can be achieved.
Further, an eighth aspect of the present invention is a data reproducing apparatus constituted by inputting means for inputting a waveform data to be reproduced, waveform equalizing means for equalizing an input waveform to an equalization reference of Partial Response Class 1 and data detecting means for detecting data from an equalized waveform, wherein:
the waveform equalizing means prevents a phase variation at a high frequency region by executing emphasis of the high frequency region and steep attenuation at a vicinity of a Nyquist frequency by using a phase flat filter.
The eighth aspect of the present invention is the data reproducing apparatus constituted by using the waveform equalizing apparatus according to the first aspect and higher equalization characteristic is realized.
Further, a ninth aspect of the present invention is a data reproducing apparatus constituted by inputting means for inputting a waveform data to be reproduced, waveform equalizing means for equalizing an input waveform to an equalization reference of Partial Response Class 1 and data detecting means for detecting data from an equalized waveform, wherein:
the waveform equalizing means is constituted by a combination of an integrator for emphasizing a low frequency region and an equalizer for equalizing to an equalization reference of Partial Response Class 4.
The ninth aspect of the present invention is the data reproducing apparatus constituted by using the waveform equalizing apparatus according to the second aspect and higher equalization characteristic is realized.
Still other objects, characteristics and advantages of the present invention will become apparent by a further detailed description based on embodiments and attached drawings of the present invention, mentioned later.